Battery charge protection system

ABSTRACT

A system comprises a battery including one or more cells, an energy source, a load, and a battery protection circuit coupled to the battery, the energy source and the load. The circuit determines if the charge of each cell is at/above a predetermined, band gap supplied threshold voltage, which results in disconnecting of the battery from the energy source. The circuit also may determine if the charge of any cell is at/below a second predetermined level, which may result in disconnecting of the battery from the load. The circuit may be radiation-hardened (e.g., via redundancy), through the use of two sets of field effect transistors, two logic gates, two groups of comparator circuits, and two relays. The circuit provides multiply redundant protection comprising: redundantly assessing the overvoltage determination; redundantly triggering battery isolation; and preventing inadvertent isolation and non-charging, occurring absent overvoltage, through redundant first and second relays.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/366,596, filed Feb. 6, 2012, which claims priority on U.S.Provisional Application Ser. No. 61/440,135 filed on Feb. 7, 2011, thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to electronic circuits, and in particular,to a circuit configured to monitor the charge of one or more cells in abattery and to prevent the charge of each cell from exceeding, and insome instances also falling below, predetermined charge levels.

BACKGROUND OF THE INVENTION

Electronic apparatuses that cannot be continuously coupled to stationarypower sources may instead employ localized sources of energy likebatteries. The growing popularity of mobile apparatuses for use incommunication, productivity, entertainment, etc. is an obvious exampleof how electronic devices may utilize batteries in order to supportapparatus mobility. Batteries may be disposable or rechargeable, withtechnological development currently being focused on rechargeablesolutions in view of resource conservation efforts and user convenience.In the area of rechargeable batteries, the evolution of new batterytechnologies and compositions has yielded rechargeable batteries thatcan provide more power, longer life and faster recharge times, which hasled to the expanded implementation of rechargeable batteries in variousareas.

One technology that has seen wide acceptance is lithium-ion (Li-ion)batteries. Li-ion batteries may comprise one or more individual Li-ioncells that can typically provide long operational life and shortrecharge times that may prove to be beneficial in many applications.However, while emerging battery technologies like Li-ion compositionsmay be able to provide strong performance, these benefits come with somemaintenance requirements. For example, Li-ion battery performance may benegatively impacted by conditions where the cells in a battery areunbalanced (e.g., one cell in a battery has a higher charge than anothercell), as well as the cells being undercharged or overcharged.Undercharging Li-ion batteries can result in electrical shorts thatcause the cells to discharge to a state where it is possible the batterycannot recover (e.g., the cells will not recharge). In more extremecases, overcharging batteries can result in failures including white-hotflames or explosions that can damage equipment.

Even in view of these care requirements and potential failures,safeguards may be built into commercial apparatuses to provideprotection that, even if a failure occurs, may simply lead to theapparatus being replaced at a nominal cost. However, some batteryapplications are not quite so easy to address. For example, satellitesthat orbit the Earth supporting positioning systems (e.g., GPS),communications, military operations, etc. may also employ rechargeablebatteries (e.g., Li-ion batteries). Solar arrays in a satellite mayrecharge batteries for powering operations when sunlight is unavailable.Once a satellite goes into service, implementing fixes may be extremelydifficult or impossible. The failure of a power system in a satellitemay not only be catastrophic from the standpoint of the loss of amulti-million dollar piece of equipment, but may also put into jeopardythe mission for which the satellite is intended, which could result infurther economic losses, or even injury or loss of life (e.g., inmilitary satellite applications, in manned orbiting platforms like theInternational Space Station, etc.). The challenge presented by theexample of satellite operation is made even more problematic given theharsh environment in which satellites operate. Without the protectiongranted by the Earth's atmosphere, the typical failure modes forbatteries and related circuitry become more probable.

SUMMARY OF THE INVENTION

Various example embodiments of the present disclosure may be directed toa system and electronic apparatuses for maintaining battery operation. Asystem may comprise a battery comprising one or more cells, an energysource, a load and a circuit coupled to at least the battery, the energysource and the load. The circuit may comprise elements configured tomeasure the charge of each of the one or more cells. If it is determinedthat the charge of any of the one or more cells is at or above apredetermined charge level, the circuit may disconnect the one or morecells from the energy source. In at least one example implementation, itmay also be possible for the circuit to determine if the charge of anyof the one or more cells is at or below a second predetermined chargelevel when measuring the charge of each cell. In instances where it isdetermined that the charge measured in any of the one or more cells isat or below the second predetermined charge level, the circuit maydisconnect the one or more cells from the load.

In accordance with at least one embodiment of the present invention, theelements of the circuit may comprise a monitoring circuit correspondingto each cell and redundant relay control circuits. The monitoringcircuit may be configured to generate a certain output (e.g., a logicalone or zero) to the redundant relay control circuits if the cell isdetermined to be at or above the predetermined charge level. In analternative configuration, it may also be possible for the monitoringcircuit to further output a second certain output to a second set ofredundant relay control circuits if the cell is determined to be at orbelow a second predetermined charge level. In either configuration, themonitoring circuit may comprise at least one test injection point forcausing the circuit to operate regardless of whether the one or morecells are at or above the predetermined charge level (e.g., or at orbelow the second predetermined charge level). Either of the examplemonitoring circuits may also be implemented redundantly in the circuit,wherein there may be multiple (e.g., two) monitoring circuits for eachcell, and each example monitoring circuit may further be comprisedwithin a single electronic apparatus such as an application specificintegrated circuit (ASIC).

In at least one example implementation, disconnecting the one or morecells from the energy source may comprise actuating redundant relayscomprised within the circuit by opening at least one of two relaysarranged serially between the battery and the energy source. In asimilar operation, the one or more cells may be disconnected from theload (e.g., if any of the cells is at or below a second predeterminedenergy level) by actuating redundant relays comprised within the circuitby opening at least one of two relays arranged serially between thebattery and the load. Regardless of the particular circuitconfiguration, the circuit may further comprise at least one of resetcoil circuits or latch coil circuits configured to actuate either of thesets of redundant relays.

The foregoing summary includes example system and apparatus embodimentsthat are not intended to be limiting. The above embodiments are usedmerely to explain selected aspects or steps that may be utilized inimplementations of the present invention. However, it is readilyapparent that one or more aspects, or steps, pertaining to an exampleembodiment can be combined with one or more aspects, or steps, of otherembodiments to create new embodiments still within the scope of thepresent invention. Therefore, persons of ordinary skill in the art wouldappreciate that various embodiments of the present invention mayincorporate aspects from other embodiments, or may be implemented incombination with other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The description of the various example embodiments is explained inconjunction with appended drawings, in which:

FIG. 1 discloses an example battery overcharge protection circuit inaccordance with at least one embodiment of the present invention.

FIG. 2 an example battery cell monitoring circuit in accordance with atleast one embodiment of the present invention.

FIG. 3 discloses an alternative example battery cell monitoring circuit,including test injection and cell undercharge monitoring, in accordancewith at least one embodiment of the present invention.

FIG. 4 discloses an alternative example battery overcharge protectioncircuit in accordance with at least one embodiment of the presentinvention.

FIG. 5 discloses an alternative example battery overcharge protectioncircuit, including redundant reset and latch coils, in accordance withat least one embodiment of the present invention.

FIG. 6 discloses an alternative example battery overcharge protectioncircuit, including redundant cell monitoring circuits and dual redundantrelay control circuits, in accordance with at least one embodiment ofthe present invention.

FIG. 7 discloses an alternative example battery overcharge protectioncircuit, including redundant reset coils, latch coils, cell monitoringcircuits and dual redundant relay control circuits, in accordance withat least one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

While illustrative implementations of one or more embodiments of thepresent invention are provided below, various changes can be madetherein without departing from the spirit and scope of the invention, asdescribed in the appended claims.

In accordance with at least one embodiment of the present invention, abattery may comprise multiple cells. While a multi-cell Li-ion batterymay be utilized for the sake of explanation in the following disclosure,the various embodiments of the present invention are not intended to belimited to use with only this battery technology. The variousembodiments of the present invention may be utilized with, for example,any power source or battery technology that may impose similaroperational requirements in that the condition of the power source orbattery must be regulated in order to maintain performance, or in moreextreme cases, to avoid failure.

In the examples disclosed herein, circuits may be configured to preventa lithium-ion (Li-ion) battery, comprising one or more lithium-ion cellsthat are connected in series, from being overcharged, and in someinstances from becoming undercharged (or overly-discharged). Forexample, the voltage of each cell in a battery may be measured, and ifany measured voltage exceeds a predetermined charge level (e.g., 4.5 V),power that would normally charge the battery supplied from an externalsource (e.g., an electrical grid) or a localized alternative source(e.g., a solar panel array) may be disconnected from the battery.Disconnection from the power source prevents the total battery voltage,and thus the individual cell voltages, from increasing any further.Avoiding overcharging is very important for Li-ion batteries because,unlike other types of cells, overcharging Li-ion cells may causecatastrophic destruction of the battery (e.g., white-hot flame orexplosion) that may potentially damage the equipment in which thebattery resides. While the possibility of this failure mode is known,the manner in which designers may address battery condition maintenanceissues in Li-ion and other similar battery types may vary widelydepending on the application (e.g., cell phones, laptop computers,automobiles, satellites, etc.).

The various embodiments of the present invention, as disclosed herein,may be applied in many scenarios, but have characteristics that makethem uniquely suitable for use in satellites. Satellites are veryexpensive. The cost of a typical satellite may be in the range of $200million to $400 million. Substantially all satellites being built nowand in the foreseeable future will utilize Li-ion batteries charged froma solar array. A catastrophic failure of a Li-ion battery system in asatellite would have an excellent chance to destroy the satellite.Therefore, it would be very beneficial to provide a system that preventscatastrophic failures from occurring.

However, satellites are subject to operational conditions that makeassurances of a particular result difficult. Electronic circuits inspace are continuously subjected to radiation that is not encountered onEarth because of filtering by the Earth's atmosphere. Circuits for spaceuse must therefore have special design features to make them “radiationhardened” or “rad-hard” that render them immune to, or at least tolerantto, degradation or failure from the effects of radiation.

At least two types of radiation may impact the operation of electronicsin space: total dose radiation and single event upset (SEU). Total doseradiation may be deemed similar to X-ray radiation in the sense that ithas a long-term cumulative effect. It is measured in units of rads (orkrads). For example, an orbiting satellite might experience 100 krads oftotal dose over a ten-year mission life, which means that circuits inthe satellite that contain hundreds of bipolar (e.g., NPN or PNP)transistors are constantly exposed to radiation. The long-term effect ofthis exposure may be a substantial reduction in current gain (“hFE” or“beta”) for the bipolar transistors. For example, an NPN transistormight typically have a beta of 100 at the time of manufacture, and thisvalue may decay over time due to use, environment, etc. For earth-boundapplications, conservative worst-case designs might require thatcircuits continue to work with bipolar transistors that have betas aslow as 70. However, rad-hard designs may require circuits to work withbipolar transistors having betas as low as 10 due to continuousexposure. In order to make up for this disparity, rad-hard circuits mayneed to have substantially more transistors.

SEU is an entirely different phenomenon. SEU is caused by a single highenergy particle from space, such as a high energy proton or alphaparticle. If a high energy particle strikes an electronic circuit, itcan cause a transistor to conduct, typically for a few microseconds. Theimpact of this event depends on the circuit. Impact with a flip-flop cancause the component to change state. In RAM memory, a bit may changefrom 0 to 1, or from 1 to 0. With respect to power circuits whereseveral transistors in series between the (+) power supply and ground,if all of these transistors turned on at the same time, which couldhappen as a result of a SEU, the resulting current through thetransistors would not be limited, and could destroy the transistors.

In accordance with at least one embodiment of the present invention, theeffects of total dose and SEU radiation on a battery overcharge circuitmay be addressed through circuit design. Referring to FIG. 1, an examplecircuit 100 may comprise Li-ion battery 110 including eight cells101-108. While example battery 110 has eight cells 101-108, the variousembodiments of the present invention are not limited to implementationscontaining only one eight cell battery, and thus, may be applied tomulti-battery systems comprising more or less cells, depending upon therequirements of the application. The charge of each cell 101-108 inbattery 110 may serve as an input to the over-voltage protection (OVP)blocks 116 and 118. OVP blocks 116 and 118 are duplicates of each other,or “redundant” in that if any of the individual OVP monitoring circuitsfail, the secondary redundant circuit may continue to operate. In asatellite system, battery 110 may be charged by a solar array (notshown) coupled to battery 110 through relays K1 and K2. A batterycontrol circuit (not shown) may control the flow of energy provided bythe solar array to charge battery 110 to a voltage of about 4.1 V. Whenthe satellite passes into eclipse (e.g., the earth is positioned betweenthe satellite and the sun), battery 102 may supply power to a load(e.g., other electronic systems for control, communication, telemetry,observation, positioning, etc.). During this time the voltage of battery110 may drop to about 3.2 V. The satellite may then exit the eclipse,and battery 110 may again be charged. This charging and discharging ofbattery 110 continues to repeat indefinitely as the satellite continuesto orbit the Earth.

However, during the charge phase it may be possible for the batterycontrol circuit to malfunction (e.g., due to damage caused by total doseradiation or SEU), wherein battery 110 may continue to be charged by thesolar panels even after reaching the nominal voltage. If any cellvoltage reaches 4.6 V, the battery can explode and destroy thesatellite. OVP circuit blocks 116 and 118 may help to prevent this fromoccurring. For example, if any cell voltage reaches a predeterminedvoltage level (e.g., 4.5 V), OVP circuits in OVP circuit blocks 116 and118 may detect the condition and trigger relays K1 and/or K2 to open,disconnecting battery 110 from the energy source (e.g., solar arrays)and preventing further increases in the voltage of battery 110.

OVP blocks 116 and 118 may comprise two groups of comparator circuits(201A-208A and 201B-208B), each with 8 comparators 261A-268A and281B-288B, respectively. An example of the individual comparatorcircuits 200A-208A and 201B-208B is disclosed in FIG. 2 for monitoringof each of the cells 101-108. Each comparator circuit 200 may supply adigital output (e.g., two of the PNP transistors 230A-238A and 230B-238Bmay turn on) if its cell voltage exceeds a predetermined charge level,such as 4.5 V, as determined by a comparison of the cell voltage againsta band gap reference 220A-228A and 220B-228B. For example, if in FIG. 1cell number 6 of battery 110 exceeds 4.5 V, then the digital output ofOVP circuits 216A and 216B will both be a “1,” whereas when the voltagein cell number 6 (or any of the cells) is below the threshold, therewill be no output or the output will be a “0”. The output of thecomparators 210A-218A are supplied to a first logic gate 126, while theoutput of comparators 210B-218B are supplied to a second logic gate 128,with both sets of comparator outputs therein being subject to an “OR”operation. If any one or another of the comparators in the first groupof comparator circuits has outputted a “1,” the result of the ORoperation of the gate 126 comprises a digital signal, which will also bea “1,” and which is supplied in parallel to the gate terminals (“G”) ofboth Q1 and Q2, each of which may be a P-Channel power field effecttransistor (FET). Also, the result of the OR operation of OR gate 128comprises a digital signal that is supplied in parallel to the gateterminals of Q3 and Q4. When both Q1 and Q3 are on, this will energizethe coil of relay K1. When both Q2 and Q4 are on, this will energize K2.

Circuit 100 in FIG. 1 therefore contains multiple redundancies in orderto protect battery 102, even in the event of failures or SEU events. Forexample, coils K1 and K2 are redundant. If either the K1 or K2 coilsfail (e.g., they experience a welded contact, open coil, shorted coil,etc.), the other coil may still function to isolate the battery. Thefour power FETs Q1, Q2, Q3, and Q4 are also redundant. If any FETshorts, its series FET may prevent the relay from turning on. If any ofthe FETs opens, the two parallel FETs will allow the other relay toenergize. OVP blocks 116 and 118 are redundant. If any one comparatorfails, it may energize its two FETs. However, this alone cannot energizea relay unless a comparator in the other group also turns on. Thesefeatures apply to hard failures (e.g., a shorted FET) and SEU eventsthat are recoverable.

FIG. 3 discloses an alternative configuration for a comparator circuit.Circuit 300 may be coupled to cell 302 and may comprise resources notonly for measuring whether the voltage of battery 302 is at or above apredetermined charge level, but may also monitor whether the charge ofcell 302 is at or below a second predetermined voltage level. Inaddition to Li-ion cells being prone to explode if they are overcharged(e.g., >4.500 V), they may also have problem if they are over-discharged(e.g., the charge drops below <2.700 V). An over-discharge condition canlead to electrical shorts that may prevent the battery from recharging.While in the latter instance a battery does not burn or explode, theinability to recharge the battery may still render a device (e.g., asatellite) unusable. Therefore, it is beneficial to monitor batteriesfor instances both when cells may potentially become overcharged andalso when cells may become over-depleted.

In FIG. 3, various individual components may have values that varydepending on the application in which the circuit is being employed. Forexample, the voltage for Band Gap (BG) reference 322 may be set to1.25V. Moreover, resistor values for a circuit may also vary, but inthis example may have the following values: resistors 308 and 310 mayeach be 400K, resistor 312 may be 19.333K, resistor 314 may be 6.667K,resistor 316 may be 10K, resistors 318 and 320 may each be 8K. VBias maybe set to +1V. In operation, circuit 300 may have two comparators thatmonitor cell 302 to determine whether the charge of the cells is at orabove a first predetermined value (e.g., 4.5V) or at or below a secondpredetermined value (e.g., 2.7V). If the over-voltage condition exists(e.g., the cell is measured to be at or above 4.5V) then the firstcomparator circuit may trigger PNP transistor 306 to be activated. If anunder-voltage condition exists (e.g., the cell is measured to be at orbelow 2.7V) then the second comparator circuit may trigger PNPtransistor 304 to be activated.

The example circuit of FIG. 3 may further comprise one or more testinjection points for simulating an over-voltage or under-voltagecondition. For example, after circuit 302 has been fully assembled andtested it may then be attached to the battery. Under normalcircumstances, the circuit cannot then be tested without jeopardizingthe battery. Testing the circuit may be important for satellites,especially immediately prior to launch, in order to verify that thecircuit is working properly. Therefore, the use of these test injectionpoint, which comprise discrete inputs to the bandgap circuit, allows fortesting, even when the circuit is coupled to the battery, but withoutdisturbing the battery. These test inputs allow Ground Support Equipment(GSE) to artificially change BG reference voltage 322, and therebyartificially induce an over-voltage or under-voltage condition,simulating a failure, in order to exercise/test all of the individualvoltage sensing circuits just prior to launch.

Circuit 300 may further include digital to analog (D/A) converter 324for setting the over-voltage and/or under-voltage thresholds. The D/A(FIG. 3) serves to calibrate (or trim) the voltage threshold of thecircuit after final assembly, by adjusting the output voltage of thebandgap regulator circuit. The D/A typically has 5 bits of resolution,with a 1-bit step changing the voltage threshold by 1 mV, for a totaladjustment range of +/−16 mV. At the time of assembly, various smallerrors may be present, due to the tolerances of the fixed resistors, aswell as errors in the bandgap circuit. The worst-case threshold errordue to the cumulative effect of these errors is generally known to beless than 16 mV. Therefore, this threshold error may be compensated bysetting the D/A to the appropriate value. This may be performed byadding zero jumper wires to program the D/A.

As a more detailed example, assume that it is desired to set the voltagethreshold to exactly 4.000 V. Without the D/A converter in the circuit,the voltage thresholds for various numbers of manufactured circuitswould vary over some range, and may typically fall within a tolerance orrange of +/−10 mV from the target of 4.000 V (i.e. ranging from 3.990 Vto 4.010 V). In order to reduce this error, the D/A converter is addedto each circuit, for “trimming” the circuit after final assembly. Eachbit in the D/A moves the threshold by 1 mV (0.001 V). As part of thecalibration process of the circuit, the D/A may initially be set to itsmidpoint, which is 10000 (for a 5-bit D/A). The voltage threshold maynow be measured. If it is exactly 4.000 V, the D/A input at 10000 mayremain unchanged. However, if the voltage threshold is measured to be3.993 V, which is 7 mV less than the target of 4.000 V, the D/A inputmay be increased by 7 counts, to be 10111. This would increase thevoltage threshold by 7 mV, bringing it to the desired 4.000 V. Thevoltage threshold could then be re-measured to verify that it isactually 4.000 V. Jumper wires at the D/A input may next be soldered inplace, to permanently set the input code to 10111. This methodology for“trimming” the circuit might have been accomplished in the past using asmall potentiometer, or by soldering a “Select at Test” (SAT) resistorin place. To specify a D/A converter with the appropriate number ofbits, requires knowing the maximum range of adjustment (20 mV in theexample) and the voltage perturbation (or value) of each bit (1 mV inthe example). Then the ratio (20 in this example) can be calculated. Thenumber of bits (N) is then calculated and must be selected as follows:2^(N)>ratio. In the example, since (2)⁴=16 and (2)⁵=32, 32 was selected,because 32>20, whereas 16<20. In other words, a 4-bit (or smaller) D/Awould either have insufficient range, or insufficient resolution, so a5-bit D/A would be utilized in this example.

In accordance with at least one embodiment of the present invention, theexample circuit of FIG. 4 discloses a battery charge level protectionsystem for a satellite. The example circuit may comprise solar array 400and battery charge control 402, which may be coupled to the remainder ofthe circuit (including battery 416) via relays K1 and K2 as disclosed at404. In addition, load 416 may be coupled to the rest of the circuit(including battery 414) via relays K3 and K4. During in-light satelliteoperation, all relays may be closed and power may be supplied to bothbattery 414 and/or load 420. Card 406 may comprise a monitoring circuit414 for each cell 418 of battery 416. In at least one exampleimplementation, each monitoring circuit may be comprised within a singleapplication specific integrated circuit (ASIC). Each monitoring circuit414 may monitor the charge of each cell 418 in order to detect ifover-voltage or under-voltage conditions exist. If either conditionexists, monitoring circuit 414 corresponding to the problem cell 418 maygenerate a certain output, such as a logical 1. The outputs of allmonitoring circuits 412 may then be combined via logical OR 412 so thatif any battery cell is over-voltage or under voltage, correspondinglogic 410 (e.g., over-voltage logic, OVL, or under-voltage logic, UVL)may trigger the corresponding redundant relay control circuit 408. As aresult one or both of relays K1 and K2 may actuate (e.g., open) in anmonitored over-voltage situation, and one or both of relays K3 and K4may actuate (e.g., open) in a monitored under-voltage situation.

In at least one example implementation, the circuit of FIG. 4 mayfurther comprise reset coils 422 and latch coils 424 for forcing theactuation of relays K1 and K3. For example, reset coils 422 may causerelays K1 and/or K3 to reset (close), while latch coils 422 may causerelays K1 and K3 to latch (open). FIG. 5-7 disclose alternativeconfigurations based on the circuit disclosed in FIG. 4. For example,circuit 400 in FIG. 4 may comprise reset coils and latch coilscorresponding to each of relays K1, K2, K3 and K4, which may providefurther control in the circuit. FIG. 6 discloses an example circuit 600that comprises two identical sets of monitoring and relay controlcircuits. The configuration disclosed in FIG. 6 may improve thereliability of the battery protection circuit by providing redundancy inthe monitoring and relay triggering aspects of the circuit. If one ofthe cards fail (e.g., due to radiation exposure or an SEU), the othercard may still prevent over-voltage and under-voltage situations. Inaddition, while the redundant monitoring and relay triggering circuitsare disclosed on two separate cards, it may also be possible for asingle card to comprise both circuits. FIG. 7 combines the aspects ofFIGS. 5 and 6 into circuit 700. In particular, the additional resetcoils added in FIG. 5 and the redundant monitoring and relay triggeringcircuits introduced in FIG. 6 are both present in FIG. 7. Circuit 700 isan example of how the inclusion of redundant functionality may help toensure continuous circuit performance even in view of harsh operatingconditions like outer space.

In accordance with various embodiments of the present invention, actualbattery protection circuits may have characteristics that areparticularly suited towards the applications in which the circuit isbeing applied. Example characteristics and/or parameters that may applyto battery protection circuits being implemented in satellites includean operating temperature range of −20° C. to +60° C. The BandgapReference may have a Trim (on wafer) to 1.250 V, +1.0 mV (with D/A setto midpoint), a Temperature Stability: +4.0 mV over entire temperaturerange, a Total Dose Stability: +5.0 mV for 100 krad and an AgingStability: +5.0 mV over 15 year life. An Over-Voltage (OV) Threshold maybe set by a digital to analog (D/A) converter to 4.500 V, +2.0 mV,Temperature Stability: +12.0 mV over entire temperature range, PNP (Q1)turns on for Vcell>4.500 V and PNP (Q1) turns off for Vcell<4.300 V(hysteresis=200 mV). The D/A Converter may have 5 bits (32 levels), 1LSB moves BG output by 1.0 mV (±16 mV from midpoint). Test Injection 1(OV) when not connected (floating), has no effect. When connected toground (0 V) or to any voltage between 0V and −60 V, causes BG voltageto drop from 1.250 V to 0.75 V. (This forces an artificial OV output fortest purposes).

In an example application such as in a satellite, an under-voltage (UV)Threshold may be set in the circuit using external resistors to 2.700 V,PNP (Q2) turns on for Vcell>2.800 V, PNP (Q2) turns off for Vcell<2.700V (hysteresis=100 mV). Test Injection 2 (UV) when not connected(floating), has no effect. When connected to ground (0 V) or to anyvoltage between 0V and −60 V, causes BG voltage to increase from 1.250 Vto 2.08 V. (This forces an artificial UV output for test purposes). Whenthe comparator output is high, the PNP is off. The base-emitter resistoron the PNP must hold VBE below 0.2 V (with Icbo) over the fulltemperature range. When comparator output is low, PNP turns on.Comparator must sink adequate base current for PNP under all conditions,including low temperature (−20° C.) and low cell voltage (2.6 V). Thismust also work properly for Test Injection inputs. When the PNP is on,its Ic must be 200 uA, ±30 uA.

The Operating Voltage Range for an example battery protection circuitapplied in a satellite application may be 0 V to +7.0 V. No spuriousoutputs (from both PNP transistors) for any cell voltage (0V to +7.0 V)The Supply Current may be as low as possible (e.g., <5 mA) and the DieSize may be as small as possible in order to minimize footprint for usein satellites.

The various embodiments of the present invention are not limited only tothe examples disclosed above, and may encompass other configurations orimplementations.

For example, embodiments of the present invention may encompass a methodcomprising measuring the charge of each of one or more cells in abattery, generating a certain output if the charge of any of the one ormore cells is measured to be at or above a predetermined charge level,and, if the certain output is detected, disconnecting the battery from apower source.

For example, embodiments of the present invention may encompass anapparatus comprising means for measuring the charge of each of one ormore cells in a battery, means for generating a certain output if thecharge of any of the one or more cells is measured to be at or above apredetermined charge level, and means for, if the certain output isdetected, disconnecting the battery from a power source.

For example, embodiments of the present invention may encompasselectronic signals that cause an apparatus to measure the charge of eachof one or more cells in a battery, generate a certain output if thecharge of any of the one or more cells is measured to be at or above apredetermined charge level, and, if the certain output is detected,disconnect the battery from a power source.

For example, embodiments of the present invention may encompass a systemcomprising a battery comprising one or more cells; an energy source; aload; and a circuit coupled to at least the battery, the energy sourceand the load, the circuit comprising one or more elements configured tomeasure the charge of each of the one or more cells and to disconnectthe one or more cells from the energy source if the charge of any of theone or more cells is at or above a predetermined charge level.

The above example system may further comprise one or more elementscomprising a monitoring circuit for each cell and redundant relaycontrol circuits, the monitoring circuit being configured to generate acertain output to the redundant relay control circuits if the cell is ator above the predetermined charge level.

The above example system may be further described wherein the certainoutput is a logical one or zero.

The above example system may be further described wherein eachmonitoring circuit further comprises at least one test injection pointconfigured to accept an externally supplied voltage for causing thecircuit to operate regardless of whether the one or more cells are at orabove the predetermined charge level.

The above example system may be further described wherein the circuitfurther comprises redundant monitoring circuits for each of the one ormore cells.

The above example system may be further described wherein the monitoringcircuits are each comprised within an application specific integratedcircuit (ASIC).

The above example system may further comprise disconnecting the one ormore cells from the energy source further comprising actuating redundantrelays comprised within the circuit by opening at least one of tworelays arranged serially between the battery and the energy source.

The above example system may be further described wherein the one ormore elements further comprise at least one of reset coil circuits orlatch coil circuits configured to actuate the redundant relays.

The above example system may further comprise the one or more elementsbeing configured to disconnect the one or more cells from the load ifthe charge of any of the one or more cells is at or below a secondpredetermined charge level.

The above example system may be further described wherein the one ormore elements comprise a monitoring circuit for each cell, a first setof redundant relay control circuits and a second set of redundant relaycontrol circuits, the monitoring circuit being configured to generate afirst certain output to the first set of redundant relay controlcircuits if the cell is at or above the predetermined charge level, andto generate a second certain output to the second set of redundant relaycontrol circuits if the cell is at or below the second predeterminedcharge level.

The above example system may be further described wherein the firstcertain output is a logical one or zero and the second certain output isa logical one or zero.

The above example system may be further described wherein eachmonitoring circuit further comprises at least one test injection pointconfigured to accept an externally supplied voltage for causing thecircuit to operate regardless of whether the one or more cells are at orabove the predetermined charge level or at or below the secondpredetermined charge level.

The above example system may be further described wherein the circuitcomprises redundant monitoring circuits for each of the one or morecells.

The above example system may be further described wherein the monitoringcircuits are each comprised within an application specific integratedcircuit (ASIC).

The above example system may further comprise disconnecting the one ormore cells from the load further comprising actuating redundant relayscomprised within the circuit by opening at least one of two relaysarranged serially between the battery and the load.

The above example system may be further described wherein the one ormore elements further comprise at least one of reset coil circuits orlatch coil circuits configured to actuate the redundant relays.

For example, embodiments of the present invention may encompass anelectronic component comprising a monitoring circuit configured tomonitor a voltage and to generate a certain output if the monitoredvoltage is at or above the predetermined level; and at least one testinjection point configured to accept an externally supplied voltage forcausing the monitoring circuit to generate the certain output regardlessof whether the monitored voltage is at or above the predetermined chargelevel.

The above example electronic component may further comprise the certainoutput being a logical one or zero.

For example, embodiments of the present invention may encompass anelectronic component comprising a monitoring circuit configured tomonitor a voltage and to generate a certain output if the monitoredvoltage is at or above a predetermined voltage level and to generate asecond certain output if the monitored voltage is at or below a secondpredetermined voltage level; and at least one test injection pointconfigured to accept an externally supplied voltage for causing themonitoring circuit to generate at least one of the first certain outputor the second certain output regardless of whether the monitored voltageis at or above the predetermined voltage level or at or below the secondpredetermined voltage level.

The above example electronic component may further comprise the certainoutput being a logical one or zero.

Accordingly, it will be apparent to persons skilled in the relevant artthat various changes in form and detail can be made therein withoutdeparting from the spirit and scope of the disclosure. The breadth andscope of the present disclosure should not be limited by any of theabove-described example embodiments, but should be defined only inaccordance with the following claims and their equivalents.

What is claimed:
 1. A multiply redundant battery charge protection circuit, for use in preventing a voltage of a rechargeable battery with one or more cells from crossing a threshold voltage, said multiply redundant battery charge protection circuit comprising: a first group and a second group of comparator circuits, each said group having a respective comparator circuit for each of the one or more cells of the battery, said respective comparator circuit of each of said first and second groups configured to independently supply a digital output to indicate if the voltage of the respective cell crosses a threshold voltage; a first logic gate and a second logic gate, said first and second logic gates configured to provide a respective “or” operation for said comparator circuits of said first and second groups, each of said logic gates configured to supply a digital signal to indicate when one comparator circuit within its respective group supplies said digital output; a first transistor in parallel with a second transistor, with each said first and second transistors having its gate terminal respectively coupled to said first logic gate to receive said digital output therefrom; a third transistor in parallel with a fourth transistor, with said third and fourth transistors respectively in series with said first and second transistors, and with each said third and fourth transistors having its gate terminal respectively coupled in parallel to said second logic gate, to independently receive said digital output therefrom; and a first relay and a second relay; said first relay coupled in series with said third transistor; said second relay coupled in series with said fourth transistor; each said first and second relays comprising a respective coil configured to be energized to isolate a portion of said circuit upon either said first or said third transistor turning on after receiving said digital signal of said corresponding logic gate, or either said second or said fourth transistor turning on after receiving said digital signal of said corresponding logic gate.
 2. The multiply redundant battery charge protection circuit according to claim 1 wherein said third and fourth transistors wired respectively in series with said first and second transistors comprises each of said third and fourth transistors having a source terminal being electrically coupled to a respective drain terminal of said first and said second transistors, with said first and second transistors having a source terminal being electrically coupled to the battery positive terminal.
 3. The multiply redundant battery charge protection circuit according to claim 2 wherein said first relay being coupled in series with said third transistor comprises coupling to a drain terminal of said third transistor; and wherein said second relay being coupled in series with said fourth transistor comprises coupling to a drain terminal of said fourth transistor.
 4. The multiply redundant battery charge protection circuit according to claim 3 further comprising: a diode connected in series between said source terminal of said third transistor and said first relay, and being conductive in a direction from said third transistor to said first relay; and a diode connected in series between said source terminal of said fourth transistor and said second relay, and being conductive in a direction from said fourth transistor to said second relay.
 5. The multiply redundant battery charge protection circuit according to claim 4 further comprising: a diode coupled in parallel with said first relay to be conductive in a discharge direction; and a diode coupled in parallel with said second relay to be conductive in a discharge direction.
 6. The multiply redundant battery charge protection circuit according to claim 5 wherein said first and second groups of comparator circuits configured to independently supply said output comprise a PNP transistor being turned on by a respective comparator within each of said comparator circuits to supply said digital output; and wherein said threshold voltage for each said respective comparator is supplied by a band gap voltage reference circuit.
 7. The multiply redundant battery charge protection circuit according to claim 5 wherein each of said first and second groups of comparator circuits comprises: a first pair of comparators, said first pair of comparators configured to provide a determination of said corresponding cell being overcharged by being at or above an over-voltage threshold, and further configured to trigger a first PNP transistor to signal said respective OR gate, with the result of an “OR” operation of said respective OR gate being output to said respective coil of said first and second relays to energize said coils to disconnect the battery from the energy source; a second pair of comparators, third and fourth OR gates, and third and fourth relays; said second pair of comparators configured to provide a determination of said corresponding cell being over-discharged by being at or below a threshold over-discharge voltage, and further configured to trigger a second PNP transistor to signal a respective one of said third and fourth OR gates, with the result of an “OR” operation of said respective one of said third and fourth OR gates being output to a respective coil of said third and fourth relays to energize said coils to disconnect the battery from the load.
 8. The multiply redundant battery charge protection circuit according to claim 7, wherein said first pair of comparators comprises: a first comparator having a non-inverting input terminal coupled in series with a first resistance that is coupled in series to a band gap voltage reference circuit; and having an inverting input terminal coupled to both a positive terminal of said respective cell through a second resistance and to a negative terminal of said respective cell through a third and a fourth resistance; said first comparator having an output terminal coupled to said first PNP transistor through a fifth resistance; a second comparator having a non-inverting input terminal coupled in parallel to the output of said first comparator, and having its output terminal coupled in parallel to provide feedback to said non-inverting terminal of said first comparator through a sixth resistance; and wherein said second pair of comparators comprises: a third comparator having a non-inverting input terminal coupled in series with in series with a seventh resistance that is coupled in series to said a band gap voltage reference circuit; and having an inverting input terminal coupled to both said positive terminal of said respective cell through said second and third resistances and to said negative terminal of said respective cell through said fourth resistance; said third comparator having an output terminal coupled to said second PNP transistor through an eighth resistance; and a fourth comparator having a non-inverting input terminal coupled in parallel to the output of said third comparator, and having its output terminal coupled in parallel to provide feedback to said non-inverting terminal of said third comparator through a ninth resistance; said fourth comparator having its inverting input terminal coupled to the inverting input terminal of said second comparator with a voltage bias.
 9. The multiply redundant battery charge protection circuit according to claim 8 wherein said band gap circuit comprises a first test injection point configured to selectively cause said reference voltage of said band gap circuit to drop, to perform an overcharge test.
 10. The multiply redundant battery charge protection circuit according to claim 9 wherein said band gap circuit comprises a second test injection point configured to selectively cause said reference voltage of said band gap circuit to increase, to perform an over-discharge test.
 11. The multiply redundant battery charge protection circuit according to claim 10 further comprising a digital to analog converter configured to set said reference voltage of said hand gap circuit.
 12. The multiply redundant battery charge protection circuit according to claim 1, wherein each of said transistors is a P-Channel field effect transistor.
 13. The multiply redundant battery charge protection circuit according to claim 1 wherein said threshold voltage comprises an over-voltage threshold; and wherein said respective relay coils configured to be energized to isolate a portion of said circuit comprises said relay coils configured to be energized to disconnect the battery from the energy source.
 14. The multiply redundant battery charge protection circuit according to claim 13 wherein each of said relays further comprise a reset coil configured to cause said relays to close to reconnect the battery to the energy source, when the voltage of the respective cell drops below said over-voltage threshold.
 15. The multiply redundant battery charge protection circuit according to claim 1 wherein said threshold voltage comprises an under-voltage threshold; and wherein said respective relay coils configured to be energized to isolate a portion of said circuit comprises said relay coils configured to be energized to disconnect the battery from the load.
 16. The multiply redundant battery charge protection circuit according to claim 15 wherein each of said relays comprise a reset coil configured to cause said relays to close to reconnect the battery to the load, when the voltage of the respective cell is above said under-voltage threshold.
 17. A multiply redundant battery charge protection circuit, for use in preventing a rechargeable battery with one or more cells from being overcharged by an energy source, or from being over-discharged by a load, said multiply redundant battery charge protection circuit comprising: a first group of comparator circuits comprising a respective comparator circuit for each of the one or more cells of the battery, said comparator circuits of said first group configured to independently supply a digital output to indicate if the voltage of the respective cell is at or above an overvoltage threshold; a first logic gate configured to provide a respective “or” operation for said comparator circuits of said first group, said first logic gate configured to supply a digital signal to indicate when one comparator circuit within said first group supplies said digital output; a first transistor having its gate terminal respectively coupled to said first logic gate to receive said digital output therefrom; a first relay in series between the energy source and the battery, said first transistor coupled to a coil of said first relay, said relay coil configured to be energized to open said first relay, to disconnect the battery from the energy source, upon said first transistor turning on after receiving said digital signal from said first logic gate, to prevent the battery from being overcharged; a second group of comparator circuits comprising a respective comparator circuit for each of the one or more cells of the battery, said comparator circuits of said second group configured to independently supply a digital output to indicate if the voltage of the respective cell is at or below a threshold over-discharge voltage; a second logic gate configured to provide a respective “or” operation for said comparator circuits of said first group, said second logic gate configured to supply a digital signal to indicate when one comparator circuit within said second group supplies said digital output; a second transistor having its gate terminal respectively coupled to said second logic gate to receive said digital output therefrom; a second relay in series between the battery and the load, said second transistor coupled to a coil of said second relay, said coil of said second relay configured to be energized to open said second relay, to disconnect the battery from the load, upon said second transistor turning on after receiving said digital signal from said second logic gate, to prevent the battery from being over-discharged.
 18. The multiply redundant battery charge protection circuit according to claim 17 wherein each of said first and second relays further comprise a reset coil configured to cause said first relay to close, when the voltage of the respective cell is no longer above or above said threshold overvoltage, or close said second relay, when the voltage of the respective cell is no longer at or below said threshold over-discharge voltage.
 19. The multiply redundant battery charge protection circuit according to claim 18 wherein said first and second groups of comparator circuits configured to independently supply said output comprises a PNP transistor being turned on by a respective comparator within each of said comparator circuits to supply said digital output; and wherein said threshold voltage for each said respective comparator is supplied by a band gap voltage reference circuit.
 20. The multiply redundant battery charge protection circuit according to claim 19 wherein said band gap circuit comprises: a first test injection point configured to selectively cause said threshold overvoltage of said band gap circuit to drop, to perform an overcharge test; and a second test injection point configured to selectively cause said threshold over-discharge voltage of said band gap circuit to increase, to perform an over-discharge test.
 21. The multiply redundant battery charge protection circuit according to claim 20 further comprising a digital to analog converter configured to set said reference voltage of said band gap circuit.
 22. The multiply redundant battery charge protection circuit according to claim 17, wherein each of said transistors is a P-Channel power field effect transistor. 